need help for how to approach this question

Question 1 [Total 35 marks]

Nikita is the manager of 'Steaks Alive', a restaurant that specializes in steaks. She places a large poster on the front window which states "Free Steak! Just register in our 'Steak Eating Challenge'. If you can eat 10 steaks in one hour, they are FREE!". Kat is a steak lover and is very excited when she reads the sign. Steaks in Steaks Alive normally cost $20 each. Kat is a poor student who can never normally afford to eat steak. She enters the restaurant and asks for the challenge. Nikita sits her down at a table and begins the clock at 6pm. Sure enough, Kat manages to eat 10 steaks in 59 minutes. Nikita is shocked. She did not expect that anyone could actually meet the challenge. She promptly hands Kat an invoice for $150. Kat begins to feel ill, not just from overeating, but also the shock of being charged for all that food. When Kat complains:

(a) Nikita laughs and says "We can't afford to give away steak! Just be grateful that you got a discount of $50 for being a good sport!". Advise Kat. [12 marks]

(b) After Nikita's 'good sport' comment, Kat tries to point to the poster, but realizes it is gone. Nikita says "Yes, we withdrew that offer just after you walked in. Sorry!" Advise Kat. [23 marks]